Numerous industrial processes have an inherently high risk potential. Special pressure switches support the safety of individuals and the environment. Example: the vulcanisation of tyres for automobiles. To monitor this technique, leading manufacturers use the model MW switch from WIKA with SIL 2 rating.
Why such a pressure switch is necessary for safety in this application is shown by a look at the process: In a steam-heated press, the raw tyre is first filled with hot water to adapt it to the inner form of the press. Then, consuming pressures of around 24 bar and temperatures of 150 �C to 170 �C the vulcanisation itself occurs. Along the way, with the help of sulphur, the tyre is given its elastic and robust final shape. However, if you have no appropriate monitoring, overpressure may appear in the curing press without warning. If this happens, the chance of boiling hot steam escaping is high. To eliminate this occurrence, tyre manufacturers generally use pressure switches to ensure the safety of the process.
The model MW pressure switch with SIL 2 rating has been developed for safety-relevant applications, such as tyre vulcanisation.
Control of overpressure and interlocking
The instruments fulfil two functions simultaneously: On the main one hand, they intervene in case of overpressure, and alternatively, they control the internal interlocking of the curing press to prevent it from opening accidentally before vulcanisation is completed. The procedure is finished the moment a preset pressure value is reached. Then your pressure switch lifts the lock. This mechanism is constantly in motion in high-throughput automatic tyre production. Subsequently, the switch is continually being loaded. Consequently, it must have an extended service life as of this critical point. Premature wear would otherwise lead to an unscheduled shutdown of the plant.
Lowest failure probability
Tyre manufacturers therefore require pressure switches with distinct robustness and safety. Because of this, WIKA is rolling out the model MW pressure switch for safety-relevant applications such as vulcanisation. As a mechanical device, the model MW will switch without dependence on any energy supply, a significant safety aspect. A SIL 2 rating relative to the IEC 61508 standard certifies the functional safety of the pressure switch. Insidious can be SIL 2 certified. Thus, the expected service life is about 90,000 pressure cycles and switching operations. The chance assessment of the model MW relative to EN ISO 13849-1 by an external certification resulted in the best performance level ?PL e? (lowest failure probability).
Microswitches, also with argon filling
All model MW instruments have microswitches that switch electrical loads up to 250V AC, 20 A directly. For certain applications, microswitch versions with argon filling provide an additional boost to safety and service life. The gas reduces oxidation, protects against corrosion and prevents sparking. For low switching powers, for instance in PLC applications, there exists a variant with gold-plated contacts.
Retrofitting existing plants
The model MW safety pressure switches from WIKA are also suitable for retrofitting. In the case of tyre vulcanisation, they are able to therefore help to adapt existing installations to the specifications of DIN EN 16474, which was amended in 2015. This standard obliges tyre manufacturers to operate all new machines with improved safety technology. High Tech is supposed to avoid risks of danger in the long run.
Note
Further information on the model MW pressure switches and their safety features can be found on the WIKA website. For those who have any questions, your contact will gladly help you.
Also read our articles
SIL-certified: Functional safety with mechanical switches
Mechanical pressure switches: So how exactly does one set the switch point?